Sound Waves vs. Light Waves

Click on image for full size version (176K GIF) Photograph provided courtesy of Steve Albers

You see a flash of lightning across the night sky. Five seconds later, your hear the rumble of thunder. If lightning and thunder come from the same source, then why don't they occur at the same time?

Actually, they do occur at the same time. The time difference that you sense is due to the way sound and light travel. Light travels extremely fast (300,000,000 m/s). In fact, it is faster than anything else. Sound travels at a measly 343 m/s through air. Therefore we can see light in an instant, but it takes a while to hear thunder.

Sound has another disadvantage because it tends to bounce off molecules in the air. This makes the sound travel in all different directions. The further away the source of the sound is, the more the sound gets distorted.

Therefore, when you hear rumbling thunder, the lightning bolt was far away. When you hear a crack or boom of thunder, the lightning bolt is close to you (<100 m).